The beneficial properties of fluoropolymers, i.e. polymers having a fluorinated backbone, are well known in the art and include for example, high temperature resistance, high chemical resistance including for example high resistance to solvents, fuels and corrosive chemicals, and non-flammability. Because of these beneficial properties, fluoropolymers find wide application particularly where materials are exposed to high temperature and/or chemicals. Fluoroelastomers may be obtained upon curing or vulcanization of a fluoropolymer. Generally, fluoropolymers for making fluoroelastomers are generally amorphous polymers.
Fluoroelastomers are used in fuel management systems which include for example fuel tanks, fuel filler lines and fuel supply lines in cars or other motor vehicles because of their excellent resistance to fuels and because of the good barrier properties that can be achieved with fluoropolymers. Additionally, fluoroelastomers, may be used in a hose connecting the compressor of a turbo engine with an intercooler. Because of the high temperature of the compressed air, non-fluorine elastomers such as ethylene acrylic based elastomers or silicone elastomers cannot be used for such a hose.
Fluoropolymers are generally more expensive than non-fluorine polymers and accordingly, materials have been developed in which the fluoropolymer is used in combination with other materials to reduce the overall cost of an article. For example, in the aforementioned hose used in turbo engines, it has been proposed to use a relatively thin layer of fluoroelastomer as an inner layer of a multilayer hose where the outerlayer of the hose is then a non-fluorine elastomer such as for example a silicone elastomer. It is required in such a multilayer hose that the fluoropolymer layer be firmly and reliably bonded to the other layers of the hose. Unfortunately, bonding of a fluoroelastomer layer to other substrates is often difficult and in particular bonding to silicone elastomers has been found difficult. This is further complicated by the fact that various silicone compositions exist such that in one instance a particular fluoroelastomer composition may show good bonding, yet in another instance satisfactory bonding may not be obtained.
A further application in which a multi-layer article including a fluoropolymer layer is used is in a fuser member of a plain paper copier. Such a fuser member typically has a thermally conductive silicone elastomer which is bonded to a fluoroelastomer surface layer which may also include conductive particles. Such a fuser member is disclosed in for example U.S. Pat. No. 5,217,837. This U.S. patent describes a multilayer fuser member in which the silicone elastomer is bonded to the fluoroelastomer with the intermediate of an adhesive layer. The manufacturing of such a fuser member is unfortunately cumbersome. A similar system is described in U.S. Pat. No. 6,020,038, U.S. Pat. No. 6,096,429 and U.S. Pat. No. 6,224,978.
Fluoroelastomers may be obtained through various curing mechanisms. For example, in one method, curing of the fluoropolymer layer may be caused by a so-called peroxide curing reaction wherein the fluoropolymer includes one or more halogens such as for example bromine or iodine as cure-sites and these cure-sites are reacted with an organic peroxide whereby a three-dimensional network is created between the fluoropolymers, thereby obtaining the fluoroelastomer. Another method of curing a fluoropolymer to make a fluoroelastomer involves the use of a fluoropolymer that is capable of dehydrofluorination. Dehydrofluorination of the fluoropolymer can be effected through a dehydrofluorinating agent and the so produced reactive sites can then further react with a suitable curing agent to cause vulcanization of the fluoropolymer. The latter method is generally more cost effective as the fluoropolymers used in that method are generally less expensive than the fluoropolymers that are used in the former method. But it has also been found that fluoroelastomers that are based on a dehydrofluorination mechanism for curing are more difficult to bond to silicone rubbers.
To solve the problem of bonding a fluoroelastomer to a silicone elastomer, tie layers have been proposed between the fluoroelastomer layer and silicone elastomer layer, but this increases cost and makes the manufacturing more complicated.
WO 00/13891 discloses that improved bonding of a fluoroelastomer layer to a silicone rubber may be obtained by contacting a composition comprising (a) a fluoropolymer capable of dehydrofluorination, (b) a dehydrofluorinating agent, (c) a curing agent such as a polyhydroxy compound, (d) a coagent such as triallylisocyanurate and (e) a peroxide. Good bonding strength to a silicone rubber layer is disclosed.
JP 1995034060 discloses the addition of a silane coupling agent such as gamma-aminopropyltrimethoxysilane to a fluoroelastomer that is based on vinylidene fluoride copolymer. Improved bonding to various substrates such as metal, ceramics, concrete and natural or synthetic resin is taught.
It would now be desirable to find a further way of improving bonding of a fluoroelastomer, in particular a fluoroelastomer based on dehydrofluorination for its curing, to silicone rubbers. Preferably, this solution is cost effective, convenient and reliable. Preferably, the bond strength achieved is sufficient to allow for use in automotive applications such as fuel management systems and turbo charge hoses.